Pet Keen is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

Home > Horses > What Is the Best Age to Breed a Mare? A Complete Guide

What Is the Best Age to Breed a Mare? A Complete Guide


Vet approved

Dr. Luqman Javed Photo

Reviewed & Fact-Checked By

Dr. Luqman Javed

Veterinarian, DVM

The information is current and up-to-date in accordance with the latest veterinarian research.

Learn more »

Several important factors must be considered when breeding mares, including a conformation to accepted standards, having a sound character, strong bloodlines, and a clean bill of health. One aspect, however, is considered by many breeders to be the most important; the age of the mare being bred. What’s the best age to breed a mare? Most equine veterinarians and expert horse breeders agree that between 5 to 10 years of age is the best age to breed a mare.


There are several reasons for choosing this age as the best to breed, all of which we will look at below. Read on to get detailed information, facts, data, and more about breeding mares.

When Can a Mare Begin Breeding?

If a mare is healthy and fed a nutritious diet, most can begin breeding at 2 years of age. However, many breeders wait until a mare is at least 3 years of age before breeding them. Also, as we mentioned earlier, between 5 and 10 is accepted by most veterinarians as the best age to breed.

Horse Mare
Image By: Freddy, Pixabay

How Do You Know When a Mare Is Ready to Breed?

Mares have a 21-day ovulation cycle. During that cycle, most will be “in heat” or receptive to copulation with a stallion for about a week. Most mares will show several signs of being ready to mate, including swatting their tail, urinating when the stallion is nearby, lifting their tail, and several other receptive behaviors.

However, the best way to determine if a mare is ready to breed is by palpating (aka feeling or touching) her reproductive tract or using an ultrasound machine. The latter determines if the mare has released, or will soon release, an egg to be fertilized. A veterinarian performs both palpation and ultrasounds.

What Is a BSE?

When someone wants to breed their mare, they must evaluate the horse’s health and capacity to reproduce. A veterinarian will perform a Breeding Soundness Exam or BSE. These exams usually incorporate several types of analyses, including the following:

Examination of External Genitalia and Mammary Glands

An equine vet or theriogenologist begins a breeding soundness evaluation by inspecting the mare’s external genitalia and mammary glands. They assess these to determine if these structures appear normal. An abnormal conformation of their genitalia may lead to difficulties in both conceiving a foal and delivering it normally. Discharge from any orifice may indicate an underlying health issue that they will likely address and discuss with you before giving the mare a clean bill of health.

Rectal Palpation and Ultrasound

If the examination of the external genitalia reveals no issues, the next step is usually rectal palpation and ultrasound.These procedures are very important, so they’re often done in tandem. Palpation of the mare’s reproductive tract and its visualization with an ultrasound probe allow the vet to have a closer look at reproductive organs of interest. Information about the uterus, ovaries, and any follicles on the ovaries are key to determine if the mare has a sound reproductive tract that is suitable for breeding. Any abnormalities found are addressed and discussed with the owner.

Manual and Visual Vaginoscopy

This procedure is often done for fillies or mares that haven’t been bred. Your equine vet will look into their reproductive tract with a specialized scope to check for any abnormalities.

Uterine Culture

Uterine cultures are typically used if the breeding history of the mare in question is unknown. It can detect a uterine infection that might be problematic and decrease the mare’s fertility.

Uterine Biopsy

A uterine biopsy can detect problems that palpation might have missed. That’s because it shows the endometrium (the lining of the mare’s uterus) in microscopic detail.


Your vet may also perform blood work on your filly or mare as part of a breeding soundness evaluation. These are used to ensure that their blood parameters are within normal limits, and they don’t have any active systemic infections. Your vet may also test their blood for certain hormones that are associated with reproduction.

Other Tests

Though a breeding soundness evaluation tract assesses a mare or filly’s reproductive capability, your vet may also perform other tests on your horse. For example, issues with lameness need to be addressed, as they may hamper your horse’s reproductive capabilities.
Brown Mare Horse
Image By: jean-pierre duretz, Pixabay

What Data Should a Reproductive History Report Contain for a Mare?

To determine the reproductive health of a mare and her capability to breed, most veterinarians conduct a reproductive history by gathering historical data on the animal.

  • The mare’s age when it first had its first heat
  • The interval between the mare’s heats
  • The length of heat
  • The mare’s mothering capabilities
  • Any evidence the mare has had vaginal discharges
  • The mare’s previous milk production
  • The age that the mare was first bred
  • The mare’s breeding and foaling dates
  • The date of the mare’s last foaling
  • Whether the mare’s foaling was normal, abnormal, or assisted
  • Any teasing methods that were used
  • The number of pregnancies a mare has had
  • The breeding method used: pasture (aka natural), hand breeding, or artificial insemination

What Time of Year Is Best to Breed a Mare?

Veterinarians and breeders agree that the best time of year for a mare to foal (give birth) is from May through July. The reason for foaling during this time of year is that there’s more quality grass available for the mare to eat. The better the grass, the better the quality of the milk the mare will produce for her foal.

You should note that, in nature, the natural breeding season for mares varies depending on where they are located geographically. Most mares prefer to mate in mid to late spring. Mares aren’t receptive to breeding in winter months.

What Is Hand Breeding a Mare?

The term “hand breeding” is a bit of a misnomer. Hand breeding is when their owners bring together a mare and stallion to breed, rather than breeding naturally in the pasture (aka pasture breeding). In this way, both horses can be better controlled, and the conception rates are typically much higher.

Hand breeding also allows breeders to schedule breeding, which can be helpful when reproducing horses of high value. Lastly, hand breeding is less risky for stallions than if they breed in the pasture. Sometimes, but thankfully not often, stallions get kicked and injured by the mare during their efforts to copulate.

What Is “Teasing” a Mare?

Teasing a mare doesn’t mean making fun of her, thank goodness, but rather exposing the horse to a stallion to determine if she is receptive to copulation. In other words, a mare and a stallion are brought together, and the reaction of the mare is recorded.

This can help determine, for example, if she’s in estrus (receptive) or diestrus (not receptive). The horse used to tease a mare can be a stallion, a pony stallion, or a gelding that’s been treated with hormones.

Horse Stallion Mare
Image By: Ralph, Pixabay

When Does a Mare Become Too Old to Breed?

The peak breeding age for most mares occurs between 6 and 7 years old. At about 15 years of age, most will see a significant decline in their fertility and pregnancy rates. However, several factors impact this data. For example, a mare who has never foaled, or has only had one or two, should stop being bred at 16 years of age.

On the other hand, a mare that’s been regularly and successfully bred throughout her life can successfully become pregnant as old as 26 years of age. However, most responsible breeders won’t breed a mare after 15-16 years. Also, veterinarians agree that breeding a mare for the first time once she’s reached 14 years old is difficult and risky for her health.

How Long Are Mares Pregnant?

As we mentioned earlier, the pregnancy length for a mare is 11 months, give or take a few days. That’s why most mares are bred in late spring to foal in early spring when the grass is most abundant and nutritious.

Can a 1-Year-Old Mare get Pregnant?

The average age of puberty for a filly is 18 months, though fillies have been recorded reaching puberty as young as 10 months. While it is technically possible for a 1-year-old mare, also known as a filly, to become pregnant, it’s incredibly difficult for them to give birth to a live foal. One study, however, showed that 1-year-old mares could be successfully used as embryo donors and can help older, unsuccessful mares become pregnant.

Is 2 Years Old Too Young to Breed a Mare?

As mentioned earlier, a 2-year-old mare can become pregnant, and in the wild, it does happen. Most breeders, however, prefer to wait until a horse is significantly older for several reasons.

First, 2-year-old fillies vary widely in terms of their physical maturity. Some are more than capable of breeding, but many are not. Also, at 2 years old, many mares don’t cycle (aka go into estrus) reliably, which can make getting pregnant more difficult.


Final Thoughts

As we’ve seen, the best age to breed a mare is 5 to 10 years of age. Before then is possible, and much younger mares have successfully bred. However, mares between 5 and 10 typically are healthier, have more regular estrus cycles, and are stronger than younger fillies or mares, making the 11 months of pregnancy easier to handle.

In other words, while mares can become pregnant earlier, most veterinarians and horse breeders agree that it’s best to wait until they are at least 5 years old to begin breeding. It’s healthier for the horse and usually results in a foal being born successfully.

Featured Image Credit: Vera Zinkova, Shutterstock

Our vets

Want to talk to a vet online?

Whether you have concerns about your dog, cat, or other pet, trained vets have the answers!

Our vets